The practice of fruit thinning in stone fruit is a standard management procedure for the deciduous fruit industry. Fruit thinning is necessary since stone fruit trees tend to produce far too many blossoms each year. The excess of blossoms leads to a large quantity of fruit which is often too small to be marketable. Further, when the fruit density is too great on portions of the fruit trees, the weight of the fruit may become too large to be supported by the tree and the entire branch, including its fruit, may be lost.
Thus, the general object of chemical blossom thinning is to reduce the number of viable blossoms on a stone fruit tree during the blossom period to thereby provide a tree having a lower fruit density thereon. In this manner, overloading of sections of the tree can be avoided and larger fruit can be produced since the same amount of sustenance will be supplied to a smaller number of viable fruit.
In practice, fruit thinning is generally done by hand. In other words, workers must go to each tree and remove sufficient fruit to provide satisfactory fruit thinning. Apart from being a time consuming and labor intensive exercise, fruit thinning by hand is often very expensive.
There exist various chemicals which are currently used in the industry for blossom thinning purposes. These existing products are generally toxic to both the surrounding environment as well as the operators that are charged with the task of applying these chemical agents. Furthermore, many of the existing products are also phytotoxic to the orchard. For the above reasons, chemical blossom thinning in stone fruit has not yet become a widely used procedure.
A summary of fruit thinning methods can be found in "C.3 Uitdun Van Steenvrugte", Stadler, J. D., Navorsingsinstituut vir Vrugte en Vrugtetegnologie, Stellenbosch, South Africa, 1975. In this article both the hand thinning and chemical thinning of stone fruit are discussed. As a chemical thinning agent is disclosed DNBP (Gebutox.TM. 50% from Hoechst). It is further disclosed that this agent effectively reduces the number of blossoms on stone fruit trees and leads to increased fruit size. However, the agent has been found to be phytotoxic to the fruit trees and other plants as well. Further, the application of this agent poses some risk to the person applying it.
Another agent which has been used for fruit thinning is Paraquat.RTM.. However, this agent has been found to be toxic to humans and to cause damage to the crop treated as well as other surrounding plants. Both DNBP and Paraquat.RTM. are now withdrawn from government approval in many countries for use in blossom thinning of stone fruit for reasons of toxicological concern and orchard safety.
Accordingly, there exists a need in the stone fruit industry for a chemical blossom thinning agent which exhibits a relatively low phytotoxicity, is not harmful to humans applying the agent and is capable of providing acceptable results in blossom thinning and the subsequently required fruit thinning effect. These and other objects of the present invention will be apparent from the summary and detailed description which follow.